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The following are factors that affect the stability of Plastic Sheet Extruder:
1. Mechanical structure factors of the equipment itself:
Screw design:
Screw diameter and aspect ratio: A screw with a larger diameter and a reasonable aspect ratio can better plasticize and convey plastics, so that the material can be evenly advanced during the extrusion process. If the screw diameter is too small or the aspect ratio is inappropriate, it may lead to insufficient plasticization and unstable extrusion pressure, affecting the stability of the equipment. For example, for some high-viscosity plastic raw materials, a screw with a larger aspect ratio is required to ensure sufficient plasticization.
Screw thread structure: The screw thread shape, pitch, depth and other parameters have an important influence on the conveying and mixing effect of the material. For example, a screw with a gradual pitch can gradually compress and shear the material during the extrusion process, improve the plasticization quality and extrusion stability; while an equidistant screw is more suitable for some situations where the material conveying speed is required to be higher.
Barrel structure:
Barrel inner diameter accuracy: The dimensional accuracy of the barrel inner diameter directly affects the gap between the screw and the barrel. If the gap is too large, the material will flow back during the extrusion process, affecting the stability of the extrusion volume; if the gap is too small, the friction between the screw and the barrel will increase, resulting in increased energy consumption of the equipment, increased screw wear, and even equipment failure.
Barrel heating and cooling system distribution: The uniformity of the distribution of the heating and cooling devices on the barrel is crucial to the stability of the extruder. Uneven heating or cooling will cause uneven temperature distribution of the material in the barrel, thereby affecting the plasticization effect and extrusion stability of the plastic. For example, if the heating device is concentrated in a certain area of the barrel, the material in that area may be over-plasticized, while the material in other areas is under-plasticized.
Die design:
Die flow channel structure: The die flow channel design should ensure that the material can be evenly distributed over the entire die width, so that the thickness of the extruded sheet is uniform. Complex flow channel structure may cause poor flow of materials in the die, resulting in pressure fluctuations, affecting extrusion stability. For example, the corners of the flow channel should adopt a smooth transition to reduce the flow resistance of the material.
Temperature control of the die head: The temperature of the die head has an important influence on the molding quality and extrusion stability of the sheet. If the temperature is too high, the viscosity of the plastic melt will decrease, making the thickness of the sheet difficult to control; if the temperature is too low, the fluidity of the plastic melt will deteriorate, which may cause defects in the sheet or difficulty in extrusion.
2. Control system factors of the equipment:
Temperature control system:
The accuracy and response speed of the temperature sensor: The accuracy of the temperature sensor directly affects the measurement accuracy of the barrel and die temperature. If the accuracy of the sensor is not high, it will cause temperature control deviation, affecting the plasticization effect and extrusion stability of the plastic. Sensors with fast response speed can feedback temperature changes in time, so that the control system can quickly adjust the heating or cooling power and maintain temperature stability.
Control accuracy of heating and cooling devices: The control accuracy of heating and cooling devices determines the stability of temperature control. For example, a controller using a proportional-integral-differential (PID) control algorithm can adjust the heating or cooling power in real time according to the temperature deviation to improve the accuracy and stability of temperature control.
Speed control system:
Control accuracy of screw speed: The stability of screw speed directly affects the stability of extrusion volume. A high-precision speed control system can ensure that the screw runs stably at the set speed and avoid changes in extrusion volume due to speed fluctuations. For example, a drive system using variable frequency speed regulation technology can achieve precise control of the screw speed and can quickly adjust the speed according to production needs.
Control accuracy of traction speed: The matching degree between traction speed and extrusion speed has an important influence on the molding quality and stability of the sheet. If the traction speed is too fast, the sheet will be overstretched, resulting in thinning of the sheet and increased stress; if the traction speed is too slow, the sheet will accumulate during the extrusion process, affecting the continuity of production. Therefore, an accurate traction speed control system is required to ensure the matching of traction speed and extrusion speed.
3. Raw material factors:
Quality of raw materials:
Molecular weight distribution of plastics: Plastics with narrow molecular weight distribution have relatively stable performance and are easier to control during extrusion. Plastics with too wide molecular weight distribution have large changes in melt viscosity and fluidity, which will lead to pressure fluctuations and unstable sheet quality during extrusion.
Plastic additives: The type and amount of additives such as stabilizers, lubricants, and enhancers added to plastics also affect extrusion stability. For example, an appropriate amount of lubricant can reduce the friction between the plastic and the screw and barrel, and improve extrusion efficiency and stability; but too much lubricant may cause the melt viscosity of the plastic to decrease, affecting the molding quality of the sheet.
Dryness of raw materials: If the moisture content in the plastic raw materials is too high, bubbles and hydrolysis will occur during the extrusion process, affecting the quality and extrusion stability of the sheet. Therefore, the plastic raw materials need to be fully dried to ensure that their moisture content is within the allowable range.
4. Production process parameter factors:
Extrusion temperature: Extrusion temperature is a key parameter that affects the plasticization effect and extrusion stability of plastics. If the temperature is too high, the plastic will degrade, cross-link, and other reactions will occur, affecting the performance of the sheet; if the temperature is too low, the melt viscosity of the plastic will increase, and the extrusion pressure will increase, which may cause equipment overload or sheet defects. Therefore, it is necessary to select a suitable extrusion temperature according to the type and formula of the plastic.
Extrusion pressure: The size of the extrusion pressure directly affects the thickness and density of the sheet. If the extrusion pressure is unstable, it will lead to uneven thickness and inconsistent density of the sheet. The size of the extrusion pressure is affected by factors such as screw speed, barrel temperature, and die structure. It is necessary to adjust these parameters to ensure the stability of the extrusion pressure.
Residence time: The residence time of the plastic in the extruder has an important influence on the plasticizing effect and product quality. If the residence time is too short, the plastic may not be fully plasticized; if the residence time is too long, the plastic may suffer from overheating and degradation. Therefore, it is necessary to reasonably control the residence time of the plastic in the extruder according to the structure and production process of the equipment.
5. Equipment maintenance factors:
Regular cleaning: During the use of the extruder, plastic residues, dust and other impurities will adhere to the screw, barrel, die and other components, affecting the normal operation of the equipment. Regular cleaning of the equipment can maintain the cleanliness of the equipment and improve the operating stability of the equipment.
Wear inspection and replacement of components: Screws, barrels, bearings and other components will wear during long-term use, and severely worn components will affect the performance and stability of the equipment. Regularly check the wear of these components and replace severely worn components in time to ensure the normal operation of the equipment.
Lubrication of equipment: Regular lubrication of the equipment's transmission parts, bearings, etc. can reduce friction between parts, reduce equipment energy consumption, and improve equipment operation stability and service life.
